Conductometric study of association of lanthanum hexacyanoferrate(II) and praseodymium hexacyanoruthenate(II) in aqueous solution

Abstract

Conclusions about association and hydrolysis of trivalent cations (M3+) in the presence of cyanoferrate and cyanoruthenate were verified on solutions containing only [Me(CN)6]4- anions and M3+ cations to eliminate influence of K+ ions on the association. Owing to a partial hydrolysis of the anions during preparation of the starting salts, only the apparent stability constant of the ion pairs M3+.[Me(CN)6]4- could be evaluated, which involves a small admixture of M3+.H[Me(CN)6]3-, and further the corresponding equivalent conductivity of the pairs, λp. An abrupt decrease of log Kp values observed with KLa[Me(CN)6] after exceeding the critical dilution and attributed to hydrolysis of the M3+ cation was with the simple La3+ and Pr3+ salts similar as with double salts of La3+ and hence is not specific for the La3+ ion or for the combination M3+ + K+.